Electric control circuit



June 1948- J. L. STRATTON ,4

ELECTRIC CONTROL CIRCUIT Filed March 31, 1945 SYSTEM Inventor: Jerry Lstratton,

y HiZAttorney Patented June l, 1948 ELECTRIC CONTROL CKRCUIT Jerry L. Stratton, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 31, 1945, Serial No. 585,943

9 Claims.

My invention relates to electric control circuits and more particularly to improved electronic control circuits for controlling, indicating and measuring the pressure in high vacuum systems.

The ionization gage is perhaps the simplest means for quantitatively measuring a high vacuum. This gage, which consists essentially of a three-electrode vacuum tube, makes use of the fact that an electron emission current from a hot cathode will cause ionization of gas molecules in the tube by bombardment. The ions so produced will flow to any electrode which is maintained at a suficiently high negative potential with re spect to the hot cathode. The number of ions caused by the collision of a constant electron flow with gas molecules is a measure of the number of gas molecules present and, therefore, of the pressure in the vacuum system. A gage of this type was disclosed in a book entitled High Vacuum, by Dr. S. Dushman, which was published in 1922. The accuracy of these gages depends, among other factors, upon a constant electron flow and this usually requires, in a hot cathode device, a constant cathode heating current. Furthermore, the filament or cathode heating means is usually short lived due in part to the effect of transient electrical or pressure conditions in the system.

It is an object of my invention to provide a new and improved electric control circuit.

It is another object of my invention to provide a new and improved electric control circuit for controlling and indicating or measuring the pressure in high vacuum systems.

It is a further object of my invention to provide a new and improved electronic control circui-t for use in connection with an ionization gage which will overcome some of the disadvantages heretofore encountered inionization gages of the heated cathode type.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

The single figure of the accompanying drawing is a diagrammatic illustration of one embodiment of my invention.

Referring to the drawing, I have illustrated an ionization gage l of the hot filament type com.- prising a thermionic cathode 2, a first electrode or electron collector 3, and a second electrode or ion collector 4, all enclosed within a glass env'elope 5'. The glass envelope 5' is provided with a tubulation 6 whichis shown as connected to the desired vacuum system T. In accordance with my invention, I provide a new and improved electronic system for maintaining a constant electron emission in the ionization gage l. The source of supply for the control system may be a conventional 120 volt, cycle alternating current system represented by the supply conductors 8 which are connected through any suitable type of rectifier 9 to provide a source of direct current. The rectifier 9 comprises a transformer it] having a primary winding H connected to the A.-C. supply conductors 8 and a secondary windin I32 connected through a double-anode rectifier tube as a "bi-phase half wave rectifier. The output circuit of the rectifier 9 is connected to energize direct current supply conductors l4 and I5 of the system through a suitable filter represented by a series reactor 16 and shunt capacitors H. In order to provide a source of constant reference voltage, I utilize two glow discharge tubes !3 and 19 connected in series relation through a resistor 29 across the direct current supply conductors i l and I5. An intermediate junction terminal 2! is provided between the resistor 20 and the glow discharge tube 18 and another intermediate junction terminal 22 is provided between the glow discharge tubes F8 and [9. A voltage divider is connected across the series connected glow discharge tubes i8 and t9 and comprises two resistors 23 and 24 connected in series relation and provided with an intermediate junction terminal 25. The series connected glow tubes and voltage divider resistors 23 and 2% with the intermediate junction terminals thereof provide points of constant potential from which reference voltages are derived.

The regulated emission section of the control circuit includes an alternating source of supply which may be derived from an auxiliary secondary winding 23 provided onthetransformer f8 and a variable impedance 2?. The winding-26 is connected to energize the thermionic cathode 2, shown in the form of a filament, through the variable impedance 2?. The variable impedance 21-, as illustrated, may be a reactor of the D; C. saturable core type comprising a three-legged corestructure'i's having apair of series connected alternating current windings disposed on the outer legs oi" the core andin series relation with the filament 2 and with a direct current winding 39 on the middle leg. An electronic tubefl is connected with its anode cathode circuit in. series relation with the 11-6. winding 30 across constant potential conductor 54 and term'mal 22 of the 131-6. supply circuit to effect a variation in the current in winding 39 and thereby a variation in the impedance of the reactor 21. The tube 3| is provided with an anode 32, a cathode 33, and a control grid 34. If a pentode is used, as illustrated, the tube would also be provided with a screen grid 35 and a suppressor grid 36. The electrode 3 of the ionization tube I is connected through a resistor 37 to the junction terminal 2| of the D.-C. constant voltage supply circuit and is held at a positive potential relative to the filament 2 and the plate or collector 4. The control grid 34 of control tube 3| is connected through a resistor 38 to the junction between resistor 31 and the electrode 3 of the ionization tube. The screen grid 35 is connected to a point of constant potential, such as the junction terminal 2|, and the suppressor grid 36 is connected to the cathode in a conventional manner. The tube 3| is preferably selected to have a characteristic in which the plate current is practically constant over a range of plate voltages of the order of several hundred volts. With such a tube, small variations in plate voltage have little or no efiect on the value of the plate current which will flow through the tube. With the cathode and screen grid connected to points of constant potential, the plate current may then be made entirely dependent upon the value of the control grid voltage so that any variation in the electron fiow'in the ionization tube I which controls the control grid potential of tube 3| may be maintained at the desired constant value. of the ionization tube is connected to the negative conductor I of the filtered D.-C. supply circuit through a resistor 39 and a resistor 4|] connected in series relation in the path of the electron current of the ionization tube. The resistors 39 and 40 are provided with an intermediate junction terminal 4|. The negative conductor I5 is grounded, as indicated, at the ground connection 42. The plate 4 of the ionization tube is connected to a point which is negative with respect to its cathode 2 at another ground connection 42' through a vacuum range switch 43 comprising a plurality of resistance elements 44, 45, 4B and 41 of difierent ohmic values respectively and which are provided with a common grounded conductor for one set of corresponding terminals and an adjustable arm 48 arranged for selectively including one of the plurality of resistors 44 to 41, inclusive, in series relation with the circuit from plate 4 to the ground connection 42'. The common ground connection of the resistors 44 to 41, inclusive, is also connected to a contact terminal 49 in the vacuum range switch for cooperation with the arm 48 to permit the plate 4 to be connected directly to ground for purposes of testing the gage apparatus. The intermediate junction terminal 4| of resistors 39 and is connected to a contact terminal 59 in the vacuum range 43 so that the normal emission current of the gage may be checked in a manner to be explained later.

Since the number of ions picked up by plate 4 of the ionization tube I is proportional to the gas pressure in this tube with constant electron emission, I provide means to be responsive to this ion current for indicating and measuring the pressure or degree of vacuum in tube I and, hence, in the system I. Indication and measurement of the pressure within the ionization tube I is obtained by means of a milliammeter 5| connected to the opposite junction terminals 52 and 53 of a form of electric bridge circuit. This bridge circuit utilizes a pair of electric discharge paths in adjacent arms and, as illustrated, the discharge paths may be in a single envelope in the form of a The cathode or filament 2 twin triode 54 in which one path comprises an anode 55, a control grid 56 and a cathode 51, and in which the other path comprises an anode 58, a control grid 59 and a cathode 60. The cathodes are connected together and through an adjustable resistor 6| to the negative conductor I5 01 the filtered D.-C. supply circuit. The junction terminal 52 is connected through a fixed resistor 62 which, in turn, is connected to one terminal of an adjustable resistor 64. The junction terminal 53 is connected through a fixed resistor 63 to the opposite terminal of resistor 94. The resistor 64 is provided with an adjusting arm 64 which is in slidable engagement with resistor 64 and connected to a point of constant potential at the junction terminal 22. The grid 56 of the discharge path from anode 55 to cathode 51 is connected to the negative bus conductor I5 and this side of the bridge is used as a voltage reference. The grid 59 of the discharge path from anode 58 to cathode 60 is connected to a connection point 65 on the vacuum range switch 43 at arm 48 so that one side of the twin triode 54 is biased by the resistance drop in the vacuum gage switch and hence in accordance with the ion current of the gage.

A protective feature of the system is obtained by means of an electronic tube 65, provided with an anode 61, a cathode 68, a control grid 69, a screen grid I0 and a suppressor grid II, and having its anode-cathode circuit connected in series relation with the operating coil I2 of a relay I3 across the junction points 22 and 25 of constant potential. The screen grid I0 is connected to the point 22 of constant potential and the suppressor grid is connected to its cathode 68 in a conventional manner. The control grid 59 is connected to the terminal 65 of the vacuum range switch 43. The relay I3 is provided with normally closed contacts I4 which are in series relation with the energizing circuit of cathode 2 of the ionization tube I and normally open contacts I5 which when closed provide a self-sealing circuit for coil I2 from the D.-C. supply circuit. A manually operated normally closed switch I6, shown as a push button, is connected in series with the contacts I5 so that the relay 13 may be deenergized and allowed to return to its normal position when desired. A manually operated selective switch 11 is provided with one set of normally closed contacts I8 in series relation with the supply circuit to cathode 2 and with another set of contacts I9 which are included in series relation with a resistor for replacing in the system the filament-grid circuit of the ionization tube with the resistor 80 when contacts 18 are opened and contacts I9 are closed for the purpose of testing for leakage.

The operation of the illustrated embodiment of my invention is substantially as follows: It will be assumed that the supply circuit conductors 8 are energized and that the system is in a state of energization with current circulating through the filament 2 of the ionization tube I so that there is an electron flow from filament 2 to grid 3 and an ion current flow to plate 4. The electrons emitted from filament 2 are picked up by grid 3 and traverse a circuit from the filament 2 to grid 3 through resistor 31, to junction terminal 2|, down through glow discharge tubes I8 and I9 to the negative side of the D.-C. circuit, through resistors 40 and 39 back to the filament. This grid current of the ionization tube I produces a voltage drop across resistor 31 which applies a bias potential to regulating tube 3| of increasing 5 uesetue "p a y es th a id ent ereeses tith s tub .3! s er ahsedte ha e its h t s tent dete mined n r hr it g id het h eh a ev ous y p inted eat; any t enc in grid Pe rtiel wi ee respen sl chang th p a ent o tube 3| and thereby the current of the D.oC. control winding 313 of saturable reactor 21. Assum f r e am ha grid n f the imitati n t e tends e reese- A ncrease in this grid current will cause a greater voltage drep ee'r ss resi tor 3 eh n turn, pla s a more negative bias on the grid of tube 31. eetieh teeluee the P a e e ent o u 3 an eehe ah htlr t e ren n t l -C- e tre wi ding f setht le r a t .21 o at e h ee ehee e? rea t r 2 s ne e s su i lehtl e eem ehsete fe th en n y of fi am nt current t in reas and h em s ion will he etur ed to the neu ral e h t ht alu or w ich the system is adjusted. The ad stm n o th ys m will leeend up n, ar us c ns e a i ns but fQr one Pet fie ease i h t o e of tube 3! s conheeted. t he po 22 h ch m y b or x mpl 50 el s b lo th higher p nt p int 21 to which resistor 31 is connected, the resistor 3'! may be a 50,000 ohm resistor, Then with 3 milliamperes flowing in the grid circuit of the ionizatie tube th d 34, or the tube 3! Win have ero bias. Any variation of the grid current of the ionization tube from this value will then caus the regulati tube 3! to increase or decrease the impedance of the reactor 21 in the manner above described to efiect the desired regulating ae ieh- With the emission current constant in the ionization tube, the number of ions picked up by the plate 4 is proportional to the gas pressure in the ionization tube. The flow of ion current is through, for example, resistor 44 for the position of adjustin arm 48 as shown in the drawing, so that both the tube 66 and the anode-cathode path title-5,0 of the tube 54 are biased negatively in DIQBOrtion to the. voltage drop through resistor 4&- W th the other or left-hand anode-cathode path 55..,5,'| held at a constant grid potential and a constant voltage supply to the input terminals of the bridge circuit, the milliammeter will read a current proportional to. the ion current and hence the pressure in the ionization tube I. The voltage drop in the vacuum range switch 43 de-v pends upon the resistance tap used and the value of the ion current flow from the plate 4. The resistor 54 may be adjusted so that when there is a 1 volt drop in the vacuum range switch 43 there is 1 milliampere flowing in the milliammeter 5|. It is possible to obtain a full scale deflection on the milliammeter, depending upon the resistance tap setting used in the vacuum range switch 43. The resistor 64 may be adjusted to cause the milliammeter 5| to read zero when the drop in the vacuum switch is zero. The voltages on tube 54. are adjusted so that the tube is working over the linear portion of its characteristic whereby the reading of milliammeter 51 is a linear function of the pressure in the ionization tube I. In apparatus of this type which has been constructed, it has been found that pressures ranging from 0.01 of a micron up to 10 microns. may be read without any approximation.

The arrangement described also permits a test for emission and leakage. Normal emission under the conditions previously assumed gives an electron current in the tube I of 3 milliamperes. current, as previously traced, flows through resistor 40. in returmng to filament 2. or the eei a iou tube by cutting t e acuum switch arm 48 on the contact 50, or position, the eltaee time resls er 49 is iutredueesl in the'erid cir uit of r 5M1 tube 54. so that the emissi n can b read directl in a amount th endin up n th sel i n of he value o r sister 9- t an a umed n rma em ss on of 3 milliemnetese va ue of 200 ohms er res sto 40 w uld requ r a r ad ng o 0, milliampere t ndicate hetmal emissio In makin a eaka e te t, the s itch I! is operated t open ts contacts 1B thereby openin he filamen circuit of the ienizatio t be I and to close its contacts 19 thereby te rep ace. he ionizat on tu 1 b h fired resisto 80 whic may b or example, of the. order of 40,0 0 ohms This maintains al volta es on he ioni ation tube at their normal alue Then by selectin the p oper resistance tale of the an e switch 43, the eakage can h read on t e milli mmeter 5|, This eaka is hat f om pickup and betwe n h r d a d plate of the ionization tube I.

If a surge of pressure comes. into the ionization tube I, the ion current inc a s cau in an increase in voltage drop across the particular ree sistor then connected in the circuit of vacuum range switch 43. This increased voltage drop in resistor 44, for example, applies a more positive bias voltage to the grid of tube 66. If the surge is great enough to cause a voltage drop beyond a predetermined value, tube 66 passes enough current to pick up relay 73 so that its contacts 14 interrupt the filament circuit of the ionizae tiOIi tube 1 an the .cfl tacts 15 close a self-sealing circuit of the operating coil 72. Interruption of th filament circuit of the ionization tube cuts off the bias voltage applied to tube 54 through the range switch resistor 44 and thereby protects the milliammeter 5| from a current which would be lar e enou h to damage the meter. After the surge has subsided or has been corrected. the apparatus may be placed back in operation by operating the switch 16 which opens the selfsealin circuit of relay l3 and permits this relay to return toits normal position as illustrated in the drawing.

While I have shown and described a particular embodiment of my invention, it will occur to those skilled in the art that various changes and o fi t n may he, m de the ei w t u d par ng from m in en in s roader aspe s, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention,

W e I cl m s ne and desire. to. secure. by Letters lj-atent of the United States is:

1 In combination, an electric circuit constitute in a positive ion collector circuit, means cone nected in said electric circuit for establishing a component of voltage proportional to the ion current traversing said electric circuit, a, source of constant direct, voltage, two pairs of impedances connected across said source and connected in the form of an electric bridge, two or said impedances comprising electronic tubes connected in electrically adjacent arms of said bridge and each being provided with an anode, a cathode and a control grid, an electric circuit connection to control the potential of the control grid of one of said bridge tubes in accordance' wit-h the current of its associated anode, electric circuit means for connecting said first mentioned means in'the grid cathode circuit of said other bridge tube, and electro responsive means connected to berespcnsive to an unbalanced electrical quantity of said bridge.

2. In combination, an electric circuit constituting a positive ion collector circuit, a bias resistor connected in said electric circuit for establishing a component of voltage proportional to the ion current traversing said electric circuit, a source of constant direct voltage, two parallel connected circuits each including a series connected electronic tube and a resistance, each of said lastmentioned tubes being provided with an anode, a cathode and a control electrode, a common cathode resistor connected between the cathodes of said last-mentioned tubes and one side of said source, an adjustable resistor interconnecting said parallel circuits and having an adjustable element connected to the other side of said source, a pair of electrically opposite junction terminals between the respective tubes and said series resistors of said parallel circuits, electric circuit means for connecting the grid of one of said parallel-circuit tubes to its associated cathode through said common cathode resistor, electric circuit means for connecting the grid of the other of said parallelcircuit tubes to its associated cathode through said bias resistor and said common cathode resistor, and an electric meter connected across said pair of opposite junction terminals.

3. In combination, an ionization gage including an electronic tube comprising an evacuated envelope and having therein, a thermionic cathode, a first electrode and a second electrode, means for heating said cathode, means for maintaining the electron emission from said cathode substantiall constant, a source of constant direct voltage, circuit means for connecting said cathode and said first electrode across said source for maintaining said first electrode positive with respect to said cathode, circuit means for connecting said second electrode to said source for maintaining said second electrode negative with respect to said cathode and for establishing a closed circuit path for ion current from said second electrode to saidcathode, electroresponsive means connected to-be energized in accordance with the ion current of said electronic tube, and means responsive to the ion current of said electronic tube above a predetermined value for rendering inefiective said means for heating said cathode.

4. In combination, an ionization gage including an electronic tube comprising an evacuated envelope and having therein, a thermionic cathode, a first electrode and a second electrode, electric circuit means for heating said cathode, switching means connected in said electric circuit, means for maintaining the electron emission from said cathode substantially constant, a source of constant direct voltage, circuit means for connecting said cathode and said first electrode across said source for maintaining said first electrode positive with respect to said cathode, circuit means for connecting said second electrode to said source for maintaining said second electrode negative with respect to said cathode and for establishing a closed circuit path for ion current from said second electrode to said cathode, electroresponsive means connected to be energized in accordance with the ion current of said electronic tube, and means responsive to the ion current of said electronic tube above a predetermined value for operating said switching means to opensaid electric circuit means.

5. In combination, an ionization gage including an electronic tube comprising an evacuated envelope and having therein, a thermionic cathode including a heating electric circuit element, a first electrode and a second electrode, electric circuit means for energizing said electric circuit heater element, a relay having an operating coil and a pair of normally closed contacts in series with said electric circuit means, means for maintaining the electron emission from said cathode substantially constant, a source of constant direct voltage, circuit means for connecting said cathode and said first electrode across said source for maintaining said first electrode positive with respect to said cathode, circuit means for connecting said second electrode to said source for maintaining said second electrode negative with respect to said cathode and for establishing a closed circuit path for ion current from said second electrode to said cathode, a resistor connected in said closed circuit, an electronic tube provided with an anode, a cathode, and a control electrode and having its anodecathode circuit connected in series relation with the operating coil of said relay across said source, and means including said last mentioned resistor for interconnecting the control electrode and cathode of said last-mentioned tube.

6. In combination, an ionization gage including an electronic tube comprising an evacuated envelope and having therein a thermionic cathode including a heating electric circuit element, a first electrode and a second electrode, electric circuit means for energizing said electric circuit heater element, a relay having an operating coil and two pairs of contacts, one of said pairs of contacts being normally closed and in series relation with said electric circuit means and the other pair of contacts being normally open, means for maintaining the electron emission from said cathode substantially constant, a source of direct voltage, circuit means for connecting said cathode and said first electrode across said source for maintaining said first electrode positive with respect to said cathode, circuit means for connecting said second electrode to said source for maintaining said second electrode negative with respect to said cathode and for establishing a closed circuit path for ion current from said second electrode to said cathode, a resistor connected in said closed circuit, an electronic tube provided with an anode, a cathode, and a control electrode and having its anode-cathode circuit connected in series relation with the operating coil of said relay across said source, means including said other pair of contacts of said relay for connecting the operating coil of said relay across said source independently of said last mentioned tube upon operation of said relay to open its one pair of contacts and to close said other pair of contacts, and means for impressing a component of voltage derived from said resistor upon the control electrode of said last-mentioned tube for causing operation of'said relay to close said one set of contacts and open said other sets of contacts when said ion current is below a predetermined value and to open said one set of contacts and close said other set of contacts when said ion current is abovesaid predetermined value.

7. In combination, an ionization gage including an electronic tube comprising an evacuated envelope and having therein, a thermionic cathode, a first electrode and a second electrode, means for heating said cathode, means for maintaining the electron emission from said cathode substantially constant, a source of constant direct voltage, circuit means for connecting said cathode and said first electrode across said source for maintaining said first electrode positive with respect to said cathode, circuit means for connecting said second electrode to said source for maintaining said second electrode negative with respect to said cathode and for establishing a closed circuit path for ion current from said second electrode to said cathode, a plurality of resistor elements of difierent ohmic values, means for selectively connecting one of said resistor elements in series relation with said last mentioned circuit means, and electroresponsive means connected to be energized in accordance with the ion current of said electronic tube.

8. In combination, an ionization gage including an electronic tube comprising an evacuated envelope and having therein, a thermionic cathode, a first electrode and a second electrode, means for heating said cathode, means for maintaining the electron emission from said cathode substantially constant, a source of constant direct voltage, circuit means for connecting said cathode and said first electrode across said source for maintaining said first electrode positive with respect to said cathode, a first resistor connected in series relation with said first electrode for providing a component of voltage proportional to the electron emission current of said tube, circuit means for connecting said second electrode to said source for maintaining said second elec trode negative with respect to said cathode and for establishing a closed path for ion current from said second electrode to said cathode, a second resistor connected in series relation with said closed path for providing a component of voltage proportional to the ion current of said tube, an electric meter, an electronic tube for controlling the energization of said electric meter, and means for selectively controlling said last mentioned tube in accordance with the voltage component derived from said first resistor or from said second resistor.

9. In combination, an ionization gage including an electronic tube comprising an evacuated envelope and having therein, a thermionic cathode, a first electrode and a second electrode, an electric heating circuit for said cathode, means for maintaining the electron emission from said cathode substantially constant, a source of constant direct voltage, circuit means for connecting said cathode and said first electrode across said source for maintaining said first electrode positive with respect to said cathode, an impedance having a value equivalent to the impedance between said cathode and said first electrode, switching means having normally closed contacts in series relation with said heating circuit and normally open contacts in series relation with said resistor for selectively opening said heating circuit and inserting said resistor across said direct current source to replace the circuit from said cathode to said first electrode, circuit means for connecting said second electrode to said source for maintain- .ing said second electrode negative with respect to said cathode and for establishing a closed path for ion current from said second electrode to said cathode, a plurality of resistors having diiferent ohmic values, means for selectively connecting one of said resistors in said closed path, and electro-responsive means connected to be energized in accordance with the voltage drop of said selected resistor with said switching means having its normally closed contacts open and its normally open contacts closed.

JERRY L. STRATTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,592,364 Houskeeper (a) July 13, 1926 1,632,074 Houskeeper (b) June 14, 1927 2,023,453 Von Wedel Dec. 10, 1935 2,165,709 Killian July 11, 1939 2,236,195 McKesson Mar. 25, 1941 OTHER REFERENCES Applied Electronics, by the Elec. Engrg. Stafi of M. I. '11, page 232, John Wiley and Sons, N. Y. 0.,

1943. (Copy in Div. 54. 

